Discharge lamp having a fill including mercury and gallium iodide



July 21,1970

Original Filed Sept. 23, 1966 RELATIVE LIGHT OUT PUT IN MICHIHIRO TSUCHIHASHI ETAL 3,521,111 DISCHARGE LAMP HAVING A FILL INCLUDING MERCURY AND GALLIUM IODIDE 2 Sheets-Sheet 1 FIG. I

RELATIVE ENERGY OF' LIGHT IN MIN! | J I I I 20 4O 6O 80 400 20 4O 6 $0 5 WAVELENGTH IN m .L

END PORTION MIDDLE PORTION END PORTION July 21, 1970 Original Filed S ep t. 23. 1966 RELATIVE LIGHT OUT PUT IN :MICHlHIRO TSUCHIHASHI ETAL AND GALLIUM IODIDE FIG. 2

2 Sheets-Sheet 2 AMOUNT OF GALLIUM IODIDE IN l'flg/c;m

DISCHARGE LAMP HAVING A FILL INCLUDING MERCURY United States Patent US. Cl. 313229 2 Claims ABSTRACT OF THE DISCLOSURE A discharge lamp particularly suitable for use with blue-printing processes containing a quantity of mercury and gallium iodide in an amount of from 0.005 to 0.5, mg. for each cubic centimeter of the internal volume of its envelope for efficiently emitting the line spectra of 403 and 417 m resulting from gallium. Further, in order to ensure even printing the gallium iodide is used in an amount of up to 15% based upon the weight of the mercury charge in the lamp.

This is a continuation of our application Ser. No. 581,553 filed Sept. 23, 1966.

This invention relates in general to a mercury vapor discharge device and more particularly to such a device having a maximum light output at the wavelengths of emission spectrum in the vicinity of 400 millimicrons and especially suitable, for example, for use with a blueprinting process.

It is well known that the commercially available type of photosensitive papers used with the blueprinting process has a relatively sharp maximum sensitivity at the wavelengths of emission spectrum in the order of 400 m On the other hand, the prior art type of mercury vapor discharge lamps commonly used with the blueprinting process having a mercury vapor under from 0.5 to 1.0 atmospheric pressure at their operating temperature has three sharp emission lines at the wavelengths of 365, 405 and 436 mg respectively among which the emission line at 365 my has the highest energy. However, such mercury vapor discharge lamps are less effective for use asa light source associated with the blueprinting process because the wavelength of 365 m at which the lamps have the maximum light output is clearly apart from the wavelength of 400 m at which the ordinary photosensitive papers have the maximum sensitivity. As a result the mercury vapor discharge lamps as above described have naturally a low efficiency as far as printing is concerned.

Accordingly, the chief object of the invention is to eliminate the abovementioned disadvantage ofthe conventional mercury vapor discharge lamps referred to.

An object of the invention is to provide a new and improved mercury vapor discharge device providing a light output having the wavelengths of emission spectrum adjacent to 400 m at a high level and having a high efiiciency of printing as compared with the prior art type of mercury vapor discharge devices used for printing purposes.

3,521,111 Patented July 21, 1970 Another object of the invention is to provide a new and improved mercury vapor discharge device suitable for use with a blueprinting process and capable of producing a light output uniformity through the length of an envelope for the device to minimize localization of a light emitting portion thereof commonly known as the emission deviation whereby the entire area of a photosensitive paper to be exposed is evenly exposed to the luminant device.

With the above cited objects, the invention resides in a mercury vapor discharge device comprising a cylindrical envelope composed of a light transparent, substantially nonfusible material and closed at both ends, a pair of discharge electrodes disposed within the envelope at both ends, and a predetermined amount of mercury and an inert gas are contained in the envelope, the envelope containing therein gallium iodide in an amount of from 0.005 to 0.5 mg. per each cubic centimeter of the internal volume of the envelope.

Further objects and advantages of the invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings in which:

FIG. 1 is a spectral emission response to a mercury vapor discharge device constructed in accordance with the teachings of the invention;

FIG. 2 is a graph plotting a content of gallium iodide in the device of the invention against a light output;

FIG. 3 is a front view of a mercury vapor discharge device constructed in accordance with the teachings of the prior art and in its operating condition;

FIG. 4 is a front view of a mercury vapor discharge device constructed in accordance with the teachings of the invention and in its operating condition; and

FIG. 5 is a graph illustrating a change in relative light output from the device shown in FIG. 4 along the length thereof with a weight ratio of gallium iodide to mercury chosen as a parameter.

While the invention will be herein described in terms of a light source used with the blueprinting process it is to be understood that the same is equally applicable to any photo-chemical reaction in which a light having a wavelength of the emission spectrum approximating 400 mg. is desired to be utilized.

Referring now to the drawings and in particular to FIG. 4, there is illustrated a mercury vapor discharge device constructed in accordance with the teachings of the invention. An arrangement illustrated comprises an envelope 10, for example, a length of cylindrical quartz tube having an inside diameter of 13.5 mm. and an internal volume of approximately 20 cc., and a pair of discharge electrodes 12 and 14 of the conventional design disposed within the envelope 10 at both closed ends. A distance between the pair of eelctrodes 12 and 14 may be, for example, 14 cm. The envelope 10 includes therein 20 mg. of mercury (Hg), 3.0 mg. of mercury iodide (Hgl 1.0 mg. of gallium (Ga) and an amount of argon (Ar) under a pressure of 3.57 mm. Hg. The device just illustrated has been designed and constructed to be operated with a power of 300 watts.

Upon firing the device, the mercury iodide (Hgl is first decomposed into mercury (Hg) and iodine (I through a strong heat generated in the envelope 10 due to an initial arc established between the pair of discharge electrodes 12 and 14. Then the iodine thus formed is combined with the gallium (Ga) to provide a compound existing in the form of gallium iodide (GaI within the envelope 10. The reason for which gallium iodide is formed through the process just described is that, as well known, gallium iodide (GaI per se is an extremely chemically unstable substance in air and therefore that a compound in the form of GaI is extremely difficult to be initially sealed in the envelope 10.

The mercury vapor discharge device thus produced had a spectral emission response as shown in FIG. 1 wherein the ordinate represents a relative energy of spectral line produced by the device and the abscissa represents a wavelength of the emission spectrum in millimicrons. From FIG. 1 it is seen that the device exhibited two sharp emission lines at the wavelengths of 403 and 417 m In other words, the maximum energy of light produced by the device has the wavelength of the emission spectrum closely approximating 400 mn at which the commercially available printing papers have their maximum sensitivity. It is therefore apparent that the present device is extremely effective for use as a light source intended to expose the printing papers to the light therefrom.

In FIG. 2, there is illustrated the relationship between the light output adjacent to the wavelength of 400 m from the device and the amount of gallium iodide existing in the envelope on the basis of equal lamp wattage. In order to plot the curve shown in FIG. 2, the light output from the device was passed to a photocell through a light filter having a light transmitting characteristic substantially identical to the photosensitive characteristics of the available blueprinting papers as an electrical output from the photocell was measured. In FIG. 2 the ordinate represents the relative light output from the device, assuming that a light output from a conventional mercury vapor discharge device as 100. The abscissa represents the amount of gallium iodide in milligrams per cubic centimeter of the internal volume of the envelope.

As shown in FIG. 2, the light output adjacent to the wavelength of 400 m progressively increased as the amount of gallium iodide existing in the envelope exceeded 0.005 mg./cm. and reached its maximum when the amount of gallium iodide ranged from 0.1 to 0.2 mg./cm. A further increase in amount of gallium iodide causes the light output to decrease gradually. It has been found that when the amount of gallium iodide exceeds a magnitude of 0.5 mg./cm. gallium iodide tends to be deposited in the form of a liquid on that portion of the internal envelope wall relatively low in temperature, resulting in light being prevented from passing through such wall portion. As a result, the device not only decreases in efiiciency but also the printing paper involved has its surface areas differently exposed to the light from the device. Thus it has been found that the amount of gallium iodide existing in the envelope should range from 0.00 5 to 0.5 mg. per cubic centimeter of the internal volume of the envelope.

As above pointed out, it was assumed that the prior art type device has a relative output of 100. Therefore FIG. 2 indicates that when used as a light source for the blueprinting process, the present device doubles in efliciency as compared with the prior art type device.

As above described, there has been provided a mercury vapor discharge device high in printing efficiency by having gallium iodide in an amount of 0.00 5 to 0.5 mg. per cubic centimeter of the internal volume of the devices envelope. The results of experiments, however, indicated that in operation an arc discharge established in the envelope does not uniformly extend through the length of the latter and the arc partially reduces in diameter or deviates from the center line because of non-uniformity of gallium iodide vapor. This phenomenon leads to a fear that the printing paper to be exposed has its areas differently exposed to light. More specifically, FIG. 3 wherein the same reference numerals designate the parts corresponding to those illustrated in FIG. 4 shows the phenomenon just described. In FIG. 3, an arc of mercury vapor 16 is established between a pair of discharge electrodes 12 and 1 4 within an envelope 10 but does not uniformly extend between both electrodes. Namely the are 16 has one portion A, for example in FIG. 3 where the gallium iodide vapor is richer than the other portion, and as a result the violet light due to gallium can be seen stronger at the portion of A reduced in diameter or width and having an annular region 18 surrounding the same and emitting violet light due to gallium.

The results of experiments indicated that whether or not this emission deviation leading to irregular exposure on the printing paper depends upon a weight ratio of gallium iodide to mercury. The results of further experiments are illustrated in FIG. 5 wherein a change in relative light output from the device is plotted against the length of the devices envelope with the ratio between weights of gallium iodide and mercury contained in the envelope used as a parameter. Dotted curve A was obtained with the ratio of weight of gallium iodide (GaI to the weight of mercury (Hg) equal to a value of 25: 100, dotted-and-dashed curve B obtained with such ratio equal to a value of 15: and solid curve C was obtained with the ratio equal to a value of 3 100.

As illustrated by curve A, 25% of gallium iodide based upon the weight of mercury provided a relative light output of approximately at one end portion of the envelope and that of approximately 90 at the other end portion resulting in a non-uniform distribution of the light output throughout the length of the envelope. On the other hand, 3% of gallium iodide based upon the Weight of mercury provided a substantially uniform light output along the length of the envelope as shown by solid curve C. The results of additional experiments indicated that up to 15% of gallium iodide based upon the weight of mercury provided a distribution of light output along the length of the envelope considered to be uniform for all practical purposes although the light output on one of the end portions was somewhat different from that on the other end portion. Therefore, it has been found that the proportion of gallium iodide should not be more than 15 based upon the weight of mercury. With the ratio between weights of gallium iodide and mercury selected as above described, the mercury vapor discharge device as operated has a blue are 16 of mercury vapor extending substantially uniformly throughout the length of an envelope 10 or between a pair of discharge electrodes 12 and 14 and substantially uniformly surrounded by an annular violet luminant region 20 due to gallium as shown in FIG. 4.

From the foregoing it will be appreciated that the objects of the invention have been accomplished by the provision of a mercury vapor discharge device including gallium iodide in an amount as previously specified.

While the invention has been illustrated and described with reference to certain preferred embodiments thereof it is to be understood that the various changes and modifications may be made without departing from the spirit and scope of the invention. For example, instead of the envelope having its dimension as previously described, the invention is equally applicable to other envelopes having various dimensions different from that specified.

What we claim and desire to be secured by Letters Patent is:

1. A mercury vapor discharge device for emitting spectral lines of 403 and 417 m for use as a source of blueprinting comprising a closed cylindrical envelope composed of a light transparent material, a pair of discharge electrodes disposed within the envelope, predetermined amounts of mercury and an inert gas contained in the envelope, and said envelope containing therein only one other constituent determining the spectral lines consisting of gallium iodide in an amount of from 0.005 to 0.5 mg. for each cubic centimeter of the internal volume of the envelope.

2. A mercury vapor discharge device for emitting spec- References Cited tral lines of 403 and 417 my comprising a closed cylindri- UNITED STATES PATENTS cal envelope composed of a light transparent material closed at both ends, a pair of discharge electrodes dis 10/1966 Smith et 3,379,916 4/1968 Delrieu et a1. 313-109 posed within the envelope at opposite ends, predetermined 5 3,384,775 5/1968, Ishler et a1 amounts of mercury and an inert gas contained in the envelope; said envelope containing therein only one other OTHER REFERENCES constituent determining the spectral lines consisting of CobinerGaseouslConductors1941, P1

galhum odide in an amount of from 0.005 to 0.5 mg, for 10 RAYMOND F HOSSFELD Primary Examiner each cubic centimeter of the mternal volume of the envelope, and the gallium iodide being present in an amount U S CL X R. of up to 15% of the weight of the mercury. 313-225, 227 

